In wireless networks, a user equipment (UE) communicates through wireless links to a network of base stations or other wireless access points connected to a telecommunications network. The wireless networks have undergone rapid development through the generations of Radio Access Technology (RAT). The initial deployment of systems using analogue modulation has been superseded by second generation (2G) digital systems such as GSM (Global System for Mobile communications), typically using GERA (GSM Enhanced Data rates for GSM Evolution Radio Access) radio access technology, and these systems have themselves been replaced by or augmented by third generation (3G) digital systems such as UMTS (Universal Mobile Telecommunications System), using the UTRA (Universal Terrestrial Radio Access) radio access technology. Third generation standards provide for a greater throughput of data than is provided by second generation systems; this trend is continued with the proposals by the Third Generation Partnership Project (3GPP) of the Long Term Evolution (LTE) system, using E-UTRA (Evolved UTRA) radio access technology, which offers potentially greater capacity and additional features compared with the previous standards.
LTE is a technology proposed by 3GPP which supports high data rate (50 Mbps UL and 100 Mbps DL) and is purely packet switched (PS) system. By nature of packet switched system, they handle bursty type of data in nature. In order to support Circuit Switched (CS) services like Short Messaging Service (SMS), voice call in a multimode device capable of LTE/3G/3G, 3GPP has come up with SMS over SGs, CS Fallback mechanism to send SMS over LTE network and fall back to 2G or 3G for voice call.
In a 3GPP based 3G/2G/LTE system, during RAT change from 3G or 2G to LTE or when UE moves from one tracking area to another tracking area which does not belong to the assigned TAI list, UE will do Normal/Combined Tracking area update procedure on LTE. TAI List indicates a list of tracking areas for which the UE doesn't need to perform a tracking area updating procedure when entered one of these TAs (in the list). The TAIs in a TAI list assigned by an (Mobility Management Entity) MME to the UE belongs to the same MME area. MME may send new Globally Unique Temporary ID (GUTI) in TAU Accept and will wait for TAU complete message. In this case, when some uplink signaling or data is triggered in UE, there might be chances that UE procedure will fail after TAU procedure due to release of NAS connection by MME. This will lead to delay in connection establishment to get the service.
Current 3GPP specification does not specify how to use existing NAS signaling connection for some pending uplink signaling like UE SMS/UE call/UE data in LTE when UE is waiting for TAU accept and active flag has not set in TAU request sent in IDLE mode.
Due to abovementioned reasons, it is evident that the existing methods fail to handle pending signaling or data by using existing NAS signaling connection which was established for TAU procedure, when UE is waiting for TAU accept.